Lithographic printing plates (after process) generally consist of ink-receptive areas (image areas) and ink-repelling areas (non-image areas). During printing operation, an ink is preferentially received in the image areas, not in the non-image areas, and then transferred to the surface of a material upon which the image is to be produced. Commonly the ink is transferred to an intermediate material called printing blanket, which in turn transfers the ink to the surface of the material upon which the image is to be produced.
At the present time, lithographic printing plates (processed) are generally prepared from lithographic printing plate precursors (also commonly called lithographic printing plates) comprising a substrate and a photosensitive coating deposited on the substrate, the substrate and the photosensitive coating having opposite surface properties. The photosensitive coating is usually a photosensitive material, which solubilizes or hardens upon exposure to an actinic radiation, optionally with further post-exposure overall treatment. In positive-working systems, the exposed areas become more soluble and can be developed to reveal the underneath substrate. In negative-working systems, the exposed areas become hardened and the non-exposed areas can be developed to reveal the underneath substrate. The exposed plate is usually developed with a liquid developer to bare the substrate in the non-hardened or solubilized areas.
On-press ink and/or fountain solution developable lithographic printing plates have been disclosed in the literature. Such plates can be directly mounted on press after exposure to develop with ink and/or fountain solution during the initial prints and then to print out regular printed sheets. No separate development process before mounting on press is needed. Among the patents describing on-press ink and/or fountain solution developable lithographic printing plates are U.S. Pat. Nos. 5,258,263, 5,516,620, 5,561,029, 5,616,449, 5,677,110, 5,811,220, 6,014,929, and 6,071,675.
Conventionally, the plate is exposed with an actinic light (usually an ultraviolet light from a lamp) through a separate photomask film having predetermined image pattern which is placed between the light source and the plate. While capable of providing plate with superior lithographic quality, such a method is cumbersome and labor intensive.
Laser sources have been increasingly used to imagewise expose a printing plate which is sensitized to a corresponding laser wavelength. This would allow the elimination of the photomask film, reducing material, equipment and labor cost.
Lithographic plates comprising on a substrate an actinic light sensitive layer and a top mask layer which is opaque to the actinic light and is capable of being removed or rendered transparent to the actinic light by a non-actinic laser radiation have been disclosed in the literature. The plate is first imagewise exposed with a non-actinic laser to remove or render transparent the mask layer in the exposed areas, and then overall exposed with the actinic light. The remaining areas of the mask layer and the non-hardened or solubilized photosensitive layer are then removed by one or more liquid development processes. Examples of such plates are described in U.S. Pat. Nos. 4,132,168, 5,858,604, and 5,922,502. While such plates are capable of digital imaging and can provide durability as good as conventional plates, they require one or more cumbersome liquid chemical processes after exposure to remove the mask layer and develop the photosensitive layer. It would be desirable if such liquid chemical processes can be eliminated or reduced in processing such a plate.
Flexographic printing plates are well known for use in letterpress printing, particularly on surfaces which are soft and easily deformable, such as cardboards and plastic films. Flexographic printing plates (processed) consist of raised image areas and non-raised non-image areas. Ink is transferred from the raised image areas to printing media. At present time, flexographic printing plates (processed) are usually made from a non-processed flexographic printing plate comprising a photopolymerizable layer on a dimensionally stable support, such as polyester film and aluminum sheet (also called flexographic printing plate).
Flexographic printing plates comprising on a support a photosensitive layer and a top infrared laser ablatable mask layer have been disclosed in the patent literature. Such plates can be exposed by first imagewise exposing with infrared laser radiation to remove the mask layer in the exposed areas and then overall exposing with an actinic radiation to harden the photosensitive layer in the laser exposed areas. The remaining areas of the mask layer and the non-hardened photosensitive layer are then removed by one or more liquid development processes. Examples of such plates are described in U.S. Pat. Nos. 5,719,009, 5,705,310, 6,037,102, and 6,020,108. While the above plates allow direct imagewise exposure with infrared laser and allow elimination of the negative film, the liquid mask layer removal process is cumbersome and generates liquid chemical waste. It would be desirable if such a liquid process can be eliminated in processing such a plate.